The invention relates to a tire having a polyurethane white sidewall especially shaped for resistance to separation.
In the tire art, the white sidewall is most frequently applied to the tire in its uncured state. The handling of light-colored materials in an environment where most other materials are darker has frequently created problems with discoloration of both materials. Sometimes elaborate and costly means have had to be adopted to keep the materials separated during their manufacture, to keep them from mutual discoloration during application to the tire, and to protect the uncured white sidewall while the tire moves to its curing stage. In curing, rubbery stocks tend to flow together, making it difficult at times to maintain the clear black-white demaraction line required. One cure for this problem has been to design the white-black sidewall combination for later grinding of the sidewall; this produces the proper demarcation line, while at the same time performing the necessary cleaning operation on the sidewall to remove stains and dirt picked up during tire-processing, and to bring out the clear white color. To maintain this clear color beyond the manufacturing-stage, and until the tire eventually is in the hands of the customer requires additional cost, materials and labor, such as in the provision of plastic coverings, tire wrappings, or protective paints.
In order to minimize or eliminate the above problems, the present invention provides a means of forming the white sidewall strip directly onto the cured tire, and in such manner that the edge of the sidewall tapers to its juncture with the margin of the containment groove in the black stock of the tire. This method elminates the handling problems of the uncured stocks and the tires. Additionally, the demarcation line formed by the present method is clear, and concentric with other tire-portions; the white sidewall is resistant to curb-scuffing and separation due to the novel meniscus shape which reduces the strain concentration at the interface between the sidewall strip and tire-groove.
It is therefore an object of the invention to provide a tire manufacturing method wherein a polyurethane stream is applied to a circumferential groove in the sidewall of a cured tire in such a way as to create a sidewall strip resistant to flexing, scuffing, separation, and soiling, and with a clear, decorative demarcation line.
According to this invention, the method comprises molding a tire with a circumferential groove in the sidewall, mounting the tire with the groove lying in a substantially horizontal plane and, while rotating the tire, directing a stream of elastomer stock into the groove, the stock being directed vertically against the bottom surface of the groove and laterally against its sides, in order to produce a sidewall strip having a concave meniscus.
In the prior art, UK patent No. 1,018,035 to Dunlop mentions applying a fluid polyurethane composition onto a cured tire sidewall by spraying, brushing or spreading, or by means of a die, and then allowing the fluid to set, forming a white sidewall; however, no specific method steps are disclosed. U.S. Pat. No. 3,648,748 to Lovell discloses coating a groove in a cured tire with a liquid polyurethane, and then curing the liquid. Again, however, no method is disclosed for applying the liquid polyurethane, nor does the finished coating have the dimensional relationship to the tire groove which is created by the instant method.